Rare earth permanent magnets have been widely used in the field of electrical and electronic apparatus utilizing their excellent magnetic characteristics and also from economical reasons, and in recent years further improvement in their performance has been required. In an R—Fe—B rare earth permanent magnet, from among rare earth permanent magnets, Nd, which is a primary element, exists in greater abundance than Sm and a great amount of Co is not utilized so that material costs are lessened while the magnetic characteristics far exceed those of rare earth cobalt magnets and an R—Fe—B rare earth permanent magnet is therefore an excellent permanent magnet.
Previously, a variety of attempts have been made to improve the magnetic characteristics of such an R—Fe—B rare earth permanent magnet. Concretely, an example wherein Co is added so that the Curie temperature is raised (see Japanese unexamined patent publication No. 64733/1984), an example wherein Ti, V, Ni, Bi and the like, are added in order to obtain a stable magnetic coercive force (see Japanese unexamined patent publication No.132104/1984), an example wherein 0.02 to 0.5 atomic % of Cu is added so that the magnetic coercive force is improved and the range of the optimum temperature for heat treatment is extended and, thereby, the efficiency of manufacture is improved (see Japanese unexamined patent publication No. 219143/1989), an example wherein 0.2 to 0.5 % by atom of Cr is added so that resistance to corrosion is improved (see Japanese unexamined patent publication No. 2 19142/1989), and the like, have been reported.
In all of the above described reports a new element is added to an R—Fe—B rare earth permanent magnet and, thereby, further improvement of magnetic characteristics has been attempted. In most cases wherein another element is newly added, however, the residual magnetic flux density (Br) is lowered even in the case that the magnetic coercive force (iHc) is increased. Accordingly, practical improvement of the magnetic characteristics has been difficult to achieve.
The purpose of the present invention is to provide a material for a rare earth permanent magnet having a high magnetic coercive force and a high residual magnetic flux density.